1. Field of the Invention
The present invention relates to a rod block monitor for monitoring withdrawal of a control rod in a nuclear reactor.
2. Related Art
In a conventional rod block monitor (RBM), during a withdrawal operation of a control rod, positional information on the control rod that is an operational target is received from a control rod operating system, and only a signal of a neutron detector that surrounds the subject control rod is selected among the received signals indicating the positional information to perform a local area mean value calculation.
Among total 16 neutron detectors four of which are built in neutron detector strings at four locales which surround the selected control rod, two are selected from each of the neutron detector string to thereby execute averaging calculation of the total eight neutron detector signals.
After the neutron detector signal is detected, the local average value of the selected neutron detector signal is compared with the nuclear reactor average power. The gain is adjusted such that the local average value and the nuclear reactor average power are set equal to each other (null sequence), and thereafter, a block level appropriate to the local average value after the gain adjustment is selected (set up). While the local average value and a block level are compared with each other, when the local average value is larger than the block level, a signal for preventing the withdrawal of the control rod and a warning signal are output.
As such an RBM, there is a boiling water reactor RBM (for example, refer to Patent Document 1: Japanese Examined Patent Application No. 8-10261).
In this way, since the conventional local area RBM cannot monitor all reactor core areas at the same time due to the limitation of hardware processing ability, the monitoring area has been determined on the basis of selection control rod position information from the control rod operation system.
For this reason, the conventional RBM cannot monitor an appropriate area when the control rod position information from the control rod operation system is not correct. Furthermore, there is a problem, for example, in that it is necessary to provide a common take-in section for selected control rod position signals between the RBM and the control rod operation system and execute a soundness confirmation test on all the selected control rod position signals for ensuring reliability of the signals.
Examples of means for solving such a problem includes a method of monitoring an average value of all the local areas around the control rod at all times without depending on the selection control rod position information from the control rod operation system (all area RBM).
With the realization of the all area RBM, the RBM can perform monitoring independent from the control rod operation system which is the monitoring target. Even if the selected control rod position signal of the control rod operation system is not correct, it is possible to avoid a non-monitoring state. In addition, the common take-in section with the control rod operation system and the corresponding soundness confirmation test are eliminated, and thus it is possible to reduce the hardware costs and test expenses related thereto.
In addition, in order to realize the all area RBM, in relation to the above-mentioned null sequence and setup execution method, the following problem need be solved.
In the conventional local area RBM, after the selection control rod position information is obtained from the control rod operation system, the null sequence and setup are executed on the local area average value of the signals from the neutron detectors surrounding the target control rod.
On the other hand, in the all area RBM, independently from the control rod operation system, all the areas are monitored regularly and continuously. Therefore, the execution timing for the null sequence and setup of the conventional local area RBM cannot be applied.